Differential regulation of eotaxin expression by IFN-gamma in airway epithelial cells.

Background: Eotaxin is a chemokine that binds with high affinity and specificity to the chemokine receptor CCR3 and plays an important role in the pathogenesis of allergic disease.
Objective: We studied the regulation of eotaxin expression by the T(H)1 cytokine IFN-gamma and analyzed its molecular mechanisms.
Methods: Levels of eotaxin mRNA and protein expression in the airway epithelial cell line BEAS-2B were determined with RT-PCR and ELISA. Mechanisms of transcriptional regulation were assessed by means of electrophoretic mobility shift assays and luciferase assay with eotaxin promoter-luciferase reporter plasmids.
Results: Although IFN-gamma did not directly induce the expression of eotaxin protein, it increased the induction by TNF-alpha when these cytokines were added simultaneously. In contrast, preincubation of cells with IFN-gamma for 24 hours profoundly inhibited the production induced by TNF-alpha. IFN-gamma did not influence the TNF-alpha-induced binding of nuclear factor kappaB to a DNA probe derived from the eotaxin promoter. IFN-gamma did not increase the ability of TNF-alpha to activate the eotaxin promoter. Studies of eotaxin mRNA levels indicate that IFN-gamma combined with TNF-alpha increased the expression of eotaxin mRNA. When cells were preincubated with IFN-gamma, there was no inhibition of the appearance of eotaxin mRNA.
Conclusion: These studies demonstrate that IFN-gamma enhances eotaxin expression when added in combination with TNF-alpha and profoundly inhibits eotaxin expression after preincubation. In both cases the available data indicate that the effect is mediated by a posttranscriptional mechanism.